I am convinced that it’s important to know when you should always use a short form. In preposition: Хороша страна Америка!  (It means America is a good country NOT good country America); When a full form doesn’t exist at all: Я рад Вас видеть (I am glad to see you); Я должен это сделать (I am obliged to do that);When an adjective represents a relation between two subject or object: Сын похож на отца (The son and his father are alike); When it describes a sort or kind of something: Волки жадны (Wolfs are greedy NOT greedy wolfs);With words: такой, всякий, любой, каждый: Каждый человек красив  (every human is beautiful);

I hope it will be some of help to you in your long journey! Happy New Year!

Hello! Thanks for the question. Let’s see.  Here we have two grammatical categories: full and short form of the adjectives and the form of the adjective after «была».

Let’s start from the second one.  Even Russians every now and then ask themselves what form should they use, «был умным» or «был умный». Here I must say that Russian we know nowadays prefer to use instrumental case here. So it’s very common to say, ‘девушка была умной’. The ‘была умная’ variant is also possible, but it’s a bit old- fashioned. Say, Pushkin used it in his poems.  As for me, though I know that the second form is old-fashioned, I can easily use both in daily life or when writing something. Just remember that it’s more common today to use instrumental case here and to say, ‘Девушка была умной’.  We also use it ‘nominative case-form’ to emphasize the feature of the subject or object. For example, «Умная была девушка!» (but now she works at the grocery shop).

Okay. Let’s go to the first category of full –short forms.  In many situations you can easily use them interchangeably: «Книга интересная» –«Эта книга интересна» have the same meaning. Some books tell us that there’s a temporary criteria. For example: «Он больной» (it’s his permanent state) and «Он болен» (it’s his temporary state, he’s sick now, not always); «Он здоровый» (again he’s healthy it’s his permanent state) and «Он здоров» (he was sick but he is healthy now).  But it doesn’t work always, because we can easily say either «Он веселый or «Он всегда весел». There’s also a difference between short and full forms when we talk about an object in general or referring to a particular situation. Let me give you an example. Это короткое платье. This dress is short. In general.  It’s just a short dress. Nothing more. Это платье коротко.  This dress is short (but for whom? For me If I am tall, perhaps, to you it suits perfectly). You need to know that a short from exist only as a predicate in a sentence; it doesn’t have other cases except nominative one